ABB ArcLimiter User guide

—
TECHNICAL AND APPLICATION GUIDE
ArcLimiterTM
Arc flash mitigation solution for low
voltage equipment using UFES (ultra-
fast earthing switch)

2ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
—
Many industries are facing internal
or external deadlines to implement
arc flash (AF) mitigation solutions
within their facilities. ABB now
offers ArcLimiterTM, an arc flash
mitigation solution that is unique
in the industry. It solves the LV arc
flash problem at the MV or LV
system level.

TECHNICAL AND APPLICATION GUIDE 3
—
Table of contents
004 – 005 Introduction
006 Solidly grounded MV systems
007 – 008 Low resistance/grounded MV
systems
009 – 010 High resistance/grounded MV
systems
011 – 012 Ungrounded Delta MV systems
013 Summary of ArcLimiterTM solution
application scenarios
014 MV-LV transformers fed by MV
breaker
015 ArcLimiterTM solution application
at LV system level
016 Available UFES ratings

4ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Abbreviations used in this document
AF: arc flash
AWG: American Wire Gage
CLF: current limiting fuse
FLA: full load amperes
LV: low voltage
MV: medium voltage
PSE: primary switching element
QRU: quick release unit (of the UFES)
REA: ABB’s dedicated arc flash detection relay
SCC: short circuit capacity
SUS: secondary unit sub, MV-LV
51G: AC inverse time earth overcurrent relay
(residual method)
—
This solution is appropriate for:
- Light and heavy industrial
- Commercial facilities
- Educational campuses
- Any facility applying primary
loop fed transformers with
fused MV switches (36 kV
limit), new or existing applica-
tions
- Facilities having MV to LV
transformers in the range of
750 KVA – 5000 KVA
To prove this solution concept, tests were per-
formed at a third-party test laboratory. During an
actual LV arc flash event (performed per IEEE
C37.20.7), the REA detected and responded to the
AF event, sending a closing signal to the UFES.
The REA is advertised to detect and close its out-
put trip contact within 2.5 milliseconds (ms). With
the current setting at 1.5x the CT primary rating
and the light detection adjustment at mid-range,
this third-party test proved the REA responded
within 1 ms.
This response placed negligible voltage on the
transformer primary, extinguishing the LV arc
flash quickly (approximately 4 ms). Test results in-
dicate the incident energy level peak was 0.5 cal/
cm2, which is well below the AF threshold of 1.2
cal/cm2, where PPE is required.
A note on the CLF application is in order. A fuse
will become current limiting when the magnitude
of amperes through it is large enough to fully in-
terrupt in ¼ cycle or less, i.e., the fault waveform’s
peak is never reached. In general, for each appli-
cation with an applied UFES and MV E rated fuse,
the applying engineer needs to obtain the SCC (in
amperes) available at the upstream MV BUS. The
MV E rated fuse will reach its current limiting
threshold (¼ cycle interruption) when the ratio of
SCC to fuse full load ampere rating is 25 times at
a minimum. If the ratio is less than 25, the fuse
will take many cycles to fully interrupt. With the
UFES closed, the MV BUS is now at zero volts,
negatively impacting plant operations.
—
ArcLimiterTM
Introduction
Many industries are facing internal or external deadlines to implement
arc flash (AF) mitigation solutions within their facilities. ABB now
offers ArcLimiterTM, an arc flash mitigation solution that is unique in
the industry. It solves the LV AF problem at the MV or LV system level.
Many industries have internal distribution system configurations as
shown in Figure 1. The REA and UFES are ABB product additions to
this typical configuration that comprise the ArcLimiter AF mitigation
solution.

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
BONDING JUMPER
TECHNICAL AND APPLICATION GUIDE 5
LV starters can drop out while we are waiting for full
fuse interruption. The CLF interruption time deter-
mines when the MV BUS returns to nominal operat-
ing voltage.
Consider the following two examples for illustration
(in either case, the LV AF problem is solved equally
well):
• System SCC= 10,000A; CLF is a 150E; ratio of the
SCC to the fuse FLA rating is 67. Fuse will inter-
rupt in ¼ cycle. Operations should not be im-
pacted.
• System SCC= 4,600A; CLF is a 200E; ratio is 23.
Fuse will interrupt in cycles. Operations could be
impacted and the plant needs to be informed up-
front.
—
01 Internal distribution
system configuration
Post testing analysis revealed that MV system
grounding has an impact on overall system behavior
in case of an AF and applying a UFES. This applica-
tion note addresses system grounding configura-
tions and how to technically apply the UFES, mini-
mizing any reliability issues for customers’ plants.
Each MV grounding method is addressed.

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
BONDING JUMPER
6ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
On a solidly grounded MV system, shown in Figure
2, the ArcLimiter application for LV AF mitigation is
proven very effective by test. The UFES closes all
three phases to ground simultaneously with some
minor contact bounce. At this point, the LV AF is
over.
Depending upon UFES closing time and phase se-
quence, phases A and B fuses melt in 1 ms (MV sys-
tem voltage recovery starts) with full CLF interrup-
tion by 1.5-2 ms. The actual CLF interrupting time is
dependent upon the MV system fault availability
(many times referred to as SCC). The higher the
SCC, the faster the CLF interruption, the shorter du-
ration of the fault induced voltage dip, the less im-
pact on other on-going operations.
When phases A and B CLF fully interrupt, the entire
phase C current briefly appears as a zero sequence
current on the traces. The only path for fault current
is through the phase C fuse, to UFES phase C PSE,
to transformer grounded neutral. Since there is no
impedance in that path, the fault current flow is
high, only limited by the transformer’s short circuit
impedance.
Since phase C is delayed by 120 degrees, about 5
ms (assuming a 60 Hz system), in order for the
phase C fuse to melt, those amps will not flow via
phases A and B fuses, which are already open, but
back to the source neutral. The UFES to ground
bonding jumper can be small thermally, approxi-
mately #2 AWG, since it only has to carry current for
5 ms.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with all three
PSEs.
—
Solidly grounded MV systems
On a solidly grounded MV system, the ArcLimiter application for LV arc
flash mitigation is proven very effective by test.
—
02 solidly grounded
MV system
—
01

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
51G
BONDING JUMPER
UFES: 3 PSEs
(CLOSED)
MV “E” RATED FUSES
MV BUS (3 PHASE)
OIL or DT
XFMR
LV EQUIPMENT
(3 PHASE)
MV SWITCH
(normally closed)
REA
BONDING
JUMPER
AC
B
51G-2
51G-1
GROUND
FAULT
PATH
TECHNICAL AND APPLICATION GUIDE 7
If the MV system is not solidly grounded, but low
resistance neutral grounded (Figure 3) the applica-
tion of the ArcLimiter solution needs to change.
The UFES closes all three phases to ground, simul-
taneously, when triggered. At this point, the LV AF
is essentially over.
Depending upon UFES closing time and phase se-
quence, phase A and B fuses melt in 1 ms (MV sys-
tem voltage recovery starts) with full CLF interrup-
tion by 1.5-2 ms (SCC dependent). When phase A
and B CLF clear, the entire phase C current appears
as a zero sequence current on the test traces. There
is a large reduction in phase C fault current once
phases A and B CLF open.
The only path for fault current is through the phase
C fuse, to UFES phase C PSE, to the transformer’s
neutral, but is now limited by the source neutral re-
turn path’s resistance (Figure 4).
—
Low resistance/grounded MV
systems
If the MV system is not solidly grounded, but low resistance neutral
grounded, the application of the ArcLimiter solution needs to change.
—
03 MV system is not
solidly grounded,
but low resistance
neutral grounded
—
04 Path for fault current
is through the phase C
fuse, to UFES phase C
PSE, to the transformer’s
neutral, but is now lim-
ited by the source neutral
return path’s resistance
—
03
—
04

8ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Typically, in industrial plants, that ground fault
value can be limited to 200-600 A and in power
plants up to 1200 A. Phase C could remain energized
to the transformer primary for an extended time
and since most of the plant’s SUS are delta-wye, all
three transformer phases have the same evenly ap-
plied potential. Since there is no potential differ-
ence between the delta windings, there is no cur-
rent flow, therefore, there is no induction to
generate secondary potential. With no supporting
secondary potential, the LV AF collapses in micro-
seconds.
However, a sustained bolted line-to-ground phase C
fault on a low resistance grounded system will be
detected and tripped by the upstream 51G-1 or
51G-2 protection relay “x” seconds later. Review the
ground return path in Figure 4. This action shuts
down the entire MV BUS resulting in poor reliability
for customers’ plants. The 51G-1 or 51G-2 will be
faster than a sustained high ground fault value (say
1200 A) through the CLF.
To prevent this reliability issue, the MV SWITCH
should be installed (or retrofitted) with a shunt trip
activated by one of the QRU1’s trip out contacts
Phase A and B CLF will still interrupt in about the
same timeframe, about 1-2 ms, since they are in se-
ries through the closed PSEs. Phase C may not in-
terrupt. The upstream 51G-1 or 51G-2 will not see
ground current within its pick up range.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with the three
PSEs. The UFES to ground bonding jumper can be
small thermally, approximately #2 AWG, since it only
has to carry current for 5 ms.
—
Low resistance/grounded MV
systems

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
10A
BONDING JUMPER
UFES: 3 PSEs
(CLOSED)
MV “E” RATED FUSES
MV BUS (3 PHASE)
OIL or DT
XFMR
LV EQUIPMENT
(3 PHASE)
MV SWITCH
(normally closed)
REA
BONDING
JUMPER
AC
B
GROUND
FAULT
PATH
HIGH RESISTANCE
TECHNICAL AND APPLICATION GUIDE 9
If the MV system is high resistance neutral
grounded (Figure 5) the application of the Ar-
cLimiter solution needs to change. These types of
systems are typically applied in older industrial
plants, feeding a process. A single line to ground
fault does not cause major damage and the MV
switchgear breakers usually do not have ground
fault protection. Indications of a ground fault are
usually detected via installed voltmeters. The oper-
ating process continues as a plant benefit.
The UFES closes all three phases to ground simulta-
neously. At this point, the LV AF is essentially over.
Depending upon UFES closing time and phase se-
quence, phase A and B CLF melt in 1 ms (MV voltage
system recovery starts) with full CLF interruption
by 1.5-2 ms (SCC dependent). When phases A and B
CLF clear, the entire phase C current (now very lim-
ited) appears as a zero sequence current.
The only path for fault current is through the phase
C CLF to UFES phase C PSE to transformer’s neu-
tral, but is now very limited by the source neutral
return path’s resistance (Figure 6).
—
High resistance/grounded MV
systems
If the MV system is high resistance neutral grounded, the application of
the ArcLimiter solution needs to change.
—
05 MV system is
high resistance
neutral grounded
—
06 Path for fault current
is through the phase C
CLF to UFES phase C PSE
to transformer’s neutral,
but is now very limited
by the source neutral
return path’s resistance
—
05
—
06

10 ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Typically, in industrial plants, the maximum high im-
pedence ground fault current flow value is limited
to 10 A. Phase C could remain energized to the
transformer primary for an extended time and,
since most of the plant’s SUS are delta-wye, all
three transformer phases have the same equally ap-
plied potential. Since there is no potential differ-
ence between the delta windings, there is no cur-
rent flow, therefore, there is no induction to
generate secondary potential. With no supporting
secondary potential, the LV AF collapses in micro-
seconds.
However, having a sustained bolted line-to-ground
phase C 10 A fault will activate the plant’s ground
fault alarm system. Maintenance would be chasing
the wrong problem. To prevent this nuisance alarm,
the MV SWITCH should be installed (or retrofitted)
with a shunt trip activated by one of the QRU1’s trip
out contacts.
Two of the CLFs will still interrupt in about the same
timeframe, about 1-2 ms, Phase C CLF may not in-
terrupt. This prevents the false ground fault alarms.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with the three
PSEs. The UFES to ground bonding jumper can be
small, approximately #2 AWG, thermally, since it
only has to carry current for 5 ms.
—
High resistance/grounded MV
systems

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
BONDING JUMPER
UFES: 3 PSEs
(CLOSED)
MV “E” RATED FUSES
MV BUS (3 PHASE)
OIL or DT
XFMR
LV EQUIPMENT
(3 PHASE)
MV SWITCH
REA
BONDING
JUMPER
AC
B
TECHNICAL AND APPLICATION GUIDE 11
If the MV system is delta ungrounded (Figure 7) the
application is very similar to high resistance
grounded systems. These types of systems are
typically applied in older industrial plants feeding a
process.
A single line to ground fault does not cause any
increase in ground current to flow except from
inter-electrode capacitance. The MV switchgear
breakers do not have ground fault protection.
Indications of a ground fault are usually via
installed voltmeters. The operating process
continues as a plant benefit.
When triggered, the UFES closes all three phases to
ground simultaneously. At this point, the LV AF is
essentially over. Depending upon the UFES closing
time and phase sequence, phase A and B fuses melt
in 1 ms (MV voltage recovery starts) with full CLF
interruption by 1.5-2 ms (SCC dependent). After
phases A and B CLF clear, there is no phase C
current since the ground return path is open. See
Figure 8.
—
Ungrounded Delta MV systems
If the MV system is delta ungrounded, the application is very similar to
high resistance grounded systems.
—
07 MV system is
delta ungrounded
—
08 After phases A and
B CLF clear, there is
no phase C current
since the ground
return path is open
—
07
—
08

12 ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Phase C could remain energized to the transformer
primary for an extended time and since most of the
plant’s SUS are delta-wye, all three transformer
phases have the same equally applied potential.
Since there is no difference in potential between
the delta windings, there is no current flow, there-
fore there is no induction to generate secondary
potential.
However, having a sustained bolted line-to-ground
phase C fault will activate the plant’s ground fault
alarm system. Maintenance would be chasing the
wrong problem.
To prevent this nuisance alarm, the MV SWITCH
should be installed (or retrofitted) with a shunt trip
activated by one of the QRU1’s trip out contacts.
Two of the CLFs will still interrupt in about the same
timeframe, about 1-2 ms, Phase C CLF may not in-
terrupt. This prevents the false alarms.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with the three
PSEs. The UFES to ground bonding jumper can be
small thermally, approximately #2 AWG, since it only
has to carry current for 5 ms.
—
Ungrounded Delta MV systems

TECHNICAL AND APPLICATION GUIDE 13
—
Summary of ArcLimiterTM solution
MV application scenarios
—
Summary Table
Solidly grounded MV system
Low resistance grounded MV
system
High resistance grounded MV
system Ungrounded Delta MV system
AF is detected
UFES closes all three phases to ground simultaneously
LV AF is over
Phases A and B fuses melt in 1 ms & fully interrupt (MV system voltage recovery starts)
CLF interruption within 1.5 - 2 ms (SCC dependent)
Phase C briefly appears as a zero sequence ground current
Phase C appears as long-term flow of zero sequence ground
current
Phase C will remain energized
to the transformer primary for
an extended time
Phase C CLF interruption is delayed about 5 ms Phase C CLF interruption is delayed almost indefinitely
Too short a time for ground relay pick up
Sustained line-to-ground
phase C fault tripped by the
upstream 51G relay
Trips entire MV BUS resulting
in poor reliability for the plant
Sustained line-to-ground
phase C 10 amp fault activates
the plant’s ground fault alarm
system
Sustained line-to-ground
phase C fault will activate the
plant’s ground fault alarm
system
Maintenance would be chasing
the wrong problem
Remedy: Install MV shunt trip activated by QRU1
Two CLFs still interrupt in about the same timeframe, about 1-2 ms
Prevents upstream 51G from
tripping Prevents the false ground fault alarms
Upon UFES operation, all three fuses should be replaced, since the phase C fuse may be damaged by microsecond internal arcing, along with spent PSEs
The UFES to ground bonding jumper can be small thermally, ~#2 AWG, since it only has to carry current for 5 ms

UFES
MV SWGR BUS
OIL or DT
XFMR
LV EQUIPMENT
MV BREAKER
REA
BONDING JUMPER
ARC FLASH
50/51
HV BUS
OIL XFMR
TRIP
14 ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
The MV system may have the configuration shown
in Figure 9. The MV system grounding does not en-
ter into this application discussion because the
feeder breaker will be shunt tripped at the same
time as the UFES. Once the breaker is open, all
phase and ground current flow stops. The ground
relays have a chance to time out or pick up but do
not as the ground fault is cleared by the breaker
prior to this happening.
UFES type equipment (high speed ground
switches) have been applied for many years on LV
and MV systems to reduce arc flash incident energy
levels. They are effective but there is a concern
among some liquid-filled transformer manufactur-
ers that solving an arc flash problem with a UFES
may actually be creating a problem at the trans-
former. If the upstream HV-MV transformer is older
and/or has aged insulating paper, the high cur-
rent-induced magnetic vibrations could damage
the insulating paper causing a turn-turn trans-
former fault.
Figure 10, from IEEE C57.109, “IEEE Guide for Liquid
Immersed Transformer Through-Fault Current Du-
ration,” is a visual representation of an assumed
sustained bolted fault on the transformer’s second-
ary reflected to the primary windings. The “X” axis
is in units of times transformer’s full load amps
(base, not top). The “Y” axis, in seconds, is the time
duration capability of the transformer to thermally
and mechanically withstand a sustained secondary
bolted fault. The lower portion of the curve is the
mechanical damage area, considered the area of
most concern from a protection viewpoint.
The graph’s purpose is to assist in the coordination
of the transformer’s primary protective devices.
Even though the transformer is designed to with-
stand this long-term bolted fault level, the fault
time duration is dependent upon the device 51 pro-
tective relay settings and breaker interrupting time
frame or primary fuse interruption. The protective
device time-current-curve must be positioned left
of the transformer’s damage curve.
In order to minimize the through-fault duration, the
UFES’s shunt trip contacts should trip direct
(by-passing the 50/51 protection relay) to the up-
stream MV breaker as in Figure 9. This direct trip
action also minimizes the fault produced voltage
dip duration; a benefit to operating processes.
Upon UFES operation, all three PSEs should be re-
placed. The UFES to ground bonding jumper can be
small thermally, approximately #2 AWG; the zero se-
quence current will be zero.
—
MV-LV transformers fed by MV
breaker
—
09 MV system is not
solidly grounded,
but low resistance
neutral grounded
—
10 Path for fault current
is through the phase C
fuse, to UFES phase C
PSE, to the transformer’s
neutral, but is now lim-
ited by the source neutral
return path’s resistance
—
09
—
10

TECHNICAL AND APPLICATION GUIDE 15
If the customer does not own the MV line con-
nected to their transformer or the local utility does
not want additional products added on their MV
service line to the customer’s site, we can apply
ABB’s ArcLimiter solution to the LV transformer
side with the same arc flash mitigation effective-
ness and possibly lower installed costs. This ap-
proach should also improve MV power quality
during an AF event.
Note that in Figure 11, the CLF is now relocated
from the MV side to the LV side of the transformer.
These LV CLFs are not as long, but much wider, so
changes in mechanical installation must be consid-
ered. Connect the CLF directly to the transformer’s
secondary LV bushings. The CLF’s load terminals
should connect to the LV busduct or main load ca-
bles routed to the LV switchgear. The PSEs should
be connected from the CLF’s load terminals to
ground. The QRU100 controller can be mounted in
the LV switchgear or the transformer’s secondary
air terminal. As in the previous applications, the
REA101 needs to have communications to the
QRU100. This approach will have less negative im-
pact at the MV level.
LV fault magnitude
Once the PSEs close, the transformer and CLF will
see a bolted LV fault collapsing any LV equipment
AF. That transformer LV through-fault of 52kA will
be reflected to the MV primary as (1 / %Z) * FLA.
Example: 80% of the MV-LV transformers are
2500KVA base rated. Per ANSI, energizing the
transformer will produce an inrush of 12*FLA for
0.1s. If the transformer has an impedance of 5.75%
or 9%, the inrush will be (1 / 0.0575)*FLA =
17.4*FLA. Slightly higher than typical inrush. For
the 9%Z version, the inrush will be (1 / 0.09)*FLA =
11.1*FLA. Slightly lower than typical inrush.
Through-fault duration
A 2500KVA transformer has a top rating typically at
3333KVA (3990FLA at 480V). Therefore, a 4000A
(or 5000A) class L CLF needs to be applied. If a
Mersen A4BQ 4000A (or 5000A) is applied, that
through-fault will last 0.029s or 1.7 cycles (0.148s or
8.9 cycles). The reflected through-fault could be
higher than typical inrush but may last for less time
duration. The mix of transformer KVA vs. CLF sizes
vs. CLF response time is not that large. Each appli-
cation will have to be evaluated and the area FAE(s)
can help here.
Grounding
Similar to the MV applications, most LV applica-
tions for industrial plants have high Z (5A limited)
grounded systems. Upon PSE closure, two of the
CLFs will open, the third CLF will be damaged but
stays intact. The ground alarm will activate.
—
ArcLimiterTM solution application at
LV system level
—
11 MV system is not
solidly grounded,
but low resistance
neutral grounded
—
11

16 ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
—
Available UFES ratings
—
UFES primary switching element type U1
Electrical maximum characteristics for each voltage category (different types available)
Rated voltage (ms)* kV 1.4 17..5 27 36
Rated power frequency withstand voltage (rms) kV 542 60 70
Rated lightning impulse withstand voltage (peak) kV 12 95 150 170
Rated frequency Hz 50/60 50/60 50/60 50/60
Rated short-time withstand current kA 100 50 63 40 40
Rated peak withstand current kA 220 130 165 104 104
Rated duration of short-circuit s0.5 3 2 3 3
Rated short-curcuit making current kA 220 130 165 104 104
Mechanical properties
Dimension (diameter x height) mm (in) ~137 x 210 (~5.4" x 8.3")
Closing time ms < 1.5
Contact bounce time ms 0
Service life expectation
Number of closing operations 1
Mechanical years up to 30
Micro gas generator years up to 15
* 40.5 kV on request

—
ABB Inc.
2300 Mechanicsville Road
Florence, South Carolina 29501
Phone: +1 800 HELP 365 (option 7)
[phone]
www.abb.com/mediumvoltage
1VAL208601-TG Rev C June 2020
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